The off-spin pair will now face further scrutiny after being referred to the International Cricket Council after the second day of the second Test against India in Mumbai.
India wrapped up victory in that clash by an innings and 126 runs on Saturday, as Sachin Tendulkar made an emotional farewell from international cricket as he heads into retirement.
However, there were more pressing concerns for the West Indies, with Samuels and Shillingford now under the spotlight.
A statement released by the ICC revealed that the umpires' reports had cited concerns over the two bowlers' bowling actions after Friday's play, with particular references to Samuels' 'quicker deliveries' and Shillingford's 'doosras'.
The two players must now undergo independent analysis of their actions within 21 days, with the prospect of a suspension from bowling in international cricket.
Both Samuels and Shillingford have previously been reported and suspended for illegal bowling actions, with Samuels banned from bowling in February 2008 while Shillingford was suspended in 2010.
Both players subsequently returned to action after undergoing remedial work and further testing.
